Chiang Mai Journal of Science

Following a widespread disagreement on whether the Thai lunar calendar year 2012 is a leap-month year, qualitative and quantitative analyses were conducted to determine where the inaccuracy lies. Through in-depth studies of the Thai lunar calendar, we discovered an ancient rule used by the Suvarnabhumi civilization to determine leap-month lunar years. By observing natural occurrences, the Suvarnabhumi people were able to develop a calendar that synchronized with the seasons. This calendar is believed to have been the origin of the current Thai lunar calendar, as the two share similar characteristics. We restore the Suvarnabhumi rule and adapt it to the internationally recognized and accepted Gregorian calendar and name the resulting adaptation the “Suvarnabhumi-Gregorian” rule. We then apply the rule to reveal that the year 2012 is not a leap-month lunar year. The rule provides a more accurate way to predict leap-month lunar years while maintaining the same characteristics as the Thai lunar calendar, which should make it a welcome alternative for both academic scholars and practitioners  of traditional Thai astrology.